The present invention relates to a transmission for driving front and rear wheels of a running vehicle. More specifically, the invention relates to, a transmission in which is provided in a housing unit thereof: a hydrostatic transmission (hereinafter referred to as an HST), a front wheel driving construction, a restraint mechanism for rearward speed change, a power transmission system linking an input shaft of a power take-off shaft of the transmission with a power take-off clutch and a power take-off braking unit, and a brake operating construction which enables left and right braking units to provide oil to the vehicle independently with left and right turn brake pedals or simultaneously by a master brake pedal.
A transmission equipped with an HST and for driving front wheels and rear wheels is well-known, as disclosed in, for example, U.S. Pat. No. 5,544,547. With this technique, an engine transmits power through an input shaft to drive a hydraulic pump of the HST. The input shaft transmits the power from the rear end of the hydraulic motor of the HST to a differential gear unit, which in turn drives a gear-type speed changing unit. This unit drives the rear and front wheels through a universal joint by a fore end of the output shaft forwardly projecting from a housing.
This technique is constructed so that both the hydraulic pump and hydraulic motor are housed in the housing and the front wheels are directly driven by the output shaft of the hydraulic motor of the HST. Thus, when the speed of the gear-type speed changing unit is changed, the speed ratio between the front wheels and the rear wheels is not synchronized. In order to avoid this occurrence, a restraint mechanism must be provided which restrains the front wheels from being driven when the gear-type speed changing unit is switched to the high speed setting.
The transmission provided with the HST and gear-type speed changing unit, when the latter is switched to the high speed operating position, cannot operate a speed change pedal of the HST to increase the speed of rearward movement more than a predetermined value. This is well-known in, for example, Japanese Utility Model Publication No. Sho 62-5942.
In such a conventional technique, the restraint mechanism for rearward movement speed change with respect to the speed changing unit of the HST is constructed in such a manner that in order to change the speed of the gear-type speed changing unit, a restraint ring is interposed outside of the housing and between the operating lever and the speed changing pedal situated outside the housing. Consequently, when dust or the like attaches to the link after long use, complete restraint may not be made, resulting in a lack of reliability.
Also, the aforesaid U.S. Pat. No. 5,544,547 discloses that in a housing of a running vehicle are housed the HST, a power take-off (hereinafter referred to as a PTO) clutch, and a PTO brake unit. In detail, the housing is partitioned into a front chamber and a rear chamber. The HST is housed in the front chamber. A PTO transmission for transmitting power from an input shaft to a PTO shaft through a PTO transmission shaft onto which the PTO clutch is disposed, and the PTO brake unit for stopping the rotation of the PTO shaft, are located in the rear chamber. The PTO brake is a hydraulic actuation-type which forms a cylinder chamber on the side wall of a housing of the rear chamber. Pistons are housed in the cylinder chamber and a brake pad provided at the utmost end of a piston rod is pressed onto the outer peripheral surface of a clutch casing of the PTO clutch to thereby exert the braking action.
The brake pad, however, must strongly be pressed onto the clutch casing, whereby a large braking capacity is required to enlarge the PTO brake unit. Furthermore, the cylinder for actuating the PTO braking unit must be enlarged. Since the cylinder chamber is in the rear housing, an oil pressure supply passage for making the brake unit inactive when the PTO clutch is xe2x80x9conxe2x80x9d, is required to lead from the front housing to the rear one. As a result, the brake response is delayed due to conduit resistance. If a larger amount of inertia is mounted on the vehicle driven by the PTO shaft, the PTO clutch, when put on, is abruptly connected and applies a large force to the PTO shaft and input shaft. In such cases, the engine experiences a large shock and may stop.
On a step at one lateral side of the vehicle is disposed a running pedal for operating the HST which is forward-rearward-switchable. On the step at the other lateral side are disposed two left and right turn brake pedals independently operable of the left and right brake units provided on the vehicle. One master brake pedal is disposed in the vicinity of the running pedal, which is well-known by, for example, Japanese Patent Publication No. Hei 6-20867.
In the above-mentioned technique, a support cylinder is laterally and rotatably mounted to a support frame below the seat. The right turn brake pedal is fixed to one end of the support cylinder and a first outer cylinder is fixed to the other end. And, an abutting arm, attached to the first outer cylinder is connected with the left and right brake units. A pedal shaft is relatively rotatably fitted into the support cylinder. Onto one end of the pedal shaft is fixedly fitted a second outer cylinder on which is mounted the left turn brake pedal. The second outer cylinder connects with the left running brake unit. Thus, when the left and right turn brake pedals are trod the left and right brake units, respectively, are independently exerted. The other end of the pedal shaft outwardly projects from the first outer cylinder and provides the abutting arm. A boss portion of the master brake pedal is relatively rotatably fitted onto the support cylinder adjacent to the first outer cylinder, and an interlocking member is provided on the boss portion, so that, when the master brake pedal is trod, the interlocking member simultaneously abuts against the abutting arm of the first outer cylinder and that of the brake shaft so as to simultaneously exert the left and right brake units.
In order to stop a vehicle having a running pedal, left and right turn brake pedals and master brake pedal, an operator changes his right foot treading upon the forward or rearward running pedal to the master brake. For a nimble foot change, the master brake pedal must be easy to operate with respect to the respective running pedals. In the vehicle provided with a locking mechanism capable of fixing and releasing the running pedal in an optional forward movement operating position, when the left and right brake its equipped on the vehicle are simultaneously actuated, the locking mechanism must simultaneously be released. It is suggested that the locking mechanism be released in association with treading the master brake pedal. The conventional construction, however, sets the axis of rotation of the master brake pedal necessarily on the axis of rotation of the turn brake pedal. Therefore, the position of the master brake pedal is inevitably restricted to the running pedal or the locking mechanism, when designing the layout of the transmission.
Furthermore, the support cylinder for fixing the right turn brake is relatively rotatably fitted onto the outer periphery of the brake shaft to which the left turn brake is fixed. The cylinder fixing thereon the master brake is relatively rotatably fitted onto the outer periphery of the support cylinder. This triple construction applies a frictional force on both the brake shaft and the cylinders, for example, when the right turn brake pedal is trod to rotate the cylinder. When the outside air temperature is low and the viscosity of lubricating oil interposed between the brake shaft and the support cylinder and between the support cylinder and the cylinder is high, the frictional force is enlarged. As a result, the brake shaft and cylinder rotate together, raising the concern that both brake units might malfunction, and cause the vehicle to stop, when the vehicle is intended to be turned rightward.
In the construction such that the pedal shaft mounting thereon the left and right turn brake pedals and the pedal shaft for mounting thereon the master brake pedal are coaxially disposed, when the master brake pedal is trod, the interlocking member of the master brake pedal simultaneously strike the respective abutting arms of the left and right brake pedals. Therefore, in order to simultaneously operate the left and right brake units, the respective abutting arms and the interlocking member must accurately be positioned for mounting. When parts are processed or assembled in error, the interlocking member may mis-time the striking of the abutting arms. If the abutting arm, which strikes the interlocking member, operates one brake unit in advance, the vehicle cannot be stopped in a straight line. Moreover, even if the abutting arm is accurately positioned, the abutting arm or the interlocking member may wear due to use for long time or excessive treading. Consequently, the aforesaid timing may go wrong, making it extremely difficult to precisely adjust the brake unit.
An object of the present invention is to provide a compact transmission which can drive front wheels, rear wheels, and a PTO shaft. For this purpose, first and second chambers are formed in the front and the rear of a housing. An HST is housed in the first chamber and a gear-type speed changing unit is housed in the second chamber. Both members are connected in a driving manner. On the inner surface of a front wall constituting the first chamber is disposed a hydraulic pump and a hydraulic motor, constituting the HST. On the outer surface of the same is disposed another hydraulic pump separate from the first. A vacancy in the first chamber houses a clutch mechanism for engaging or disengaging a front wheel driving shaft with or from an output portion of the gear-type speed changing unit.
Another object of the invention is to restrain acceleration of rearward movement of the vehicle. Where the output rotation speed of the HST is changed by the gear-type speed changing unit to the high speed setting, a restraint mechanism restrains the acceleration to a predetermined speed for rearward movement. The restrain is housed in the first chamber, and makes rearward movement in the high speed setting impossible.
Still another object of the invention is to form the front wall of the housing so that the hydraulic pump and hydraulic motor are mounted on and separable from the unit.
A further object of the invention is to provide a PTO transmission. The PTO transmission unit transmits power from an engine to a PTO shaft through a PTO clutch means. On a partition between the first chamber and the second chamber is disposed a PTO brake unit, for braking the PTO shaft when the PTO clutch mechanism disconnects.
It is a still further object of the invention that left and right running brake units, equipped on the vehicle, can independently exert the braking action by treading left and right turn brake pedals, respectively. A first brake pedal shaft and a second brake pedal shaft are disposed longitudinally of the vehicle body and laterally rotatably thereof in order to make possible the simultaneous braking action by treading a master brake pedal. At one lateral end of the second brake pedal shaft are juxtaposed turn brake pedals for desirable, independent braking of the left and right running brakes. The master brake pedal is disposed at the other lateral ends of the first brake pedal shaft. At one lateral end of the first brake pedal shaft is provided a simultaneous brake operating mechanism with respect to a trip-turn brake pedal.